This invention relates to the reading of punched data from record forms. More particularly, this invention relates to apparatus and methods for the synchronous, dynamic reading of punched data cards.
The use of punches or perforations in a record form to record or store information is well known. In one widely practiced system of recording punched data, each character of information is recorded as one or more punches occupying various data locations within a columnar region of the record form. One example of such a recording system is known as the Hollerith code wherein 12 data locations are arranged in a column that extends transverse to the longitudinal dimension of the card. The data locations of a data column are punched with one or more punches to represent each digit zero to nine, each letter of the alphabet, and a number of special characters. In order to record as much information as possible on any given card size, record forms utilizing data recorded as punched columnar regions, whether utilizing the Hollerith code or other encoding techniques, generally include a number of closely spaced data columns. For example, standard tabulation cards measuring approximately 7 inches by 3 inches include 80 data columns each having 12 data locations are often used.
One type of apparatus for reading the characters on the card encoded and supplying an electrical signal representative of the encoded information is generally known as a dynamic card reader. A dynamic card reader includes an aligned array of punch sensors spaced to correspond to the spacing between the data locations within a data column. To sequentially read the character encoded in each of the successive data columns, the card is moved relative to the aligned sensors such that each passing data column is substantially in alignment with the aligned array of punch sensors. As each data column passes by the aligned array of sensors, the sensors detect the punched data locations to supply signals representing the character encoded in that data column. For example in the dynamic reading of information from the previously mentioned standard tabulation card wherein the card is encoded in Hollerith format, the card is moved past an aligned array of 12 punch sensors that are positioned to be in alignment with each of the passing data columns. As a particular data column passes the sensors, each sensor supplies a signal that indicates whether an associated data location contains a punch. Thus, it can be recognized that, in effect, the sensor array is intended to supply a 12-bit digital signal encoded in the same manner as the passing data column with the sensors sequentially supplying such a data signal as successive data columns pass by the sensor array.
A variety of punch sensors have been utilized in prior art dynamic card reading apparatus. For example, in early dynamic card readers, the punch sensors were often mechanical switch arrangements wherein electrical contact was made each time a punch passed by a sensor. In more modern dynamic card readers, optical reading means are often employed wherein one planar surface of the card is illuminated by a source of light energy and an array of optical detectors is mounted in an aligned orientation so as to be in juxtaposition with the other planar surface of the card as the card moves through the optical reading means. As the card moves past the optical array, a data punch allows light energy to be coupled to an appropriate sensor and electrical signals representing each punched data location are supplied as each data column passes by the sensor array.
Regardless of the configuration of the punch sensors, one difficulty with prior art dynamic card readers has been that the data columns on the card and the aligned sensors must be maintained in rather precise alignment with one another to prevent the generation of erroneous signals. Since the card must be moved relative to the sensor array, and since the data columns are often closely spaced to one another, prior art card readers have often been structurally complex and have often comprised a number of precision parts in order to maintain satisfactory alignment between the sensor array and the data columns.
Even though a particular dynamic card reader may maintain the card aligned such that each punched data location arrives at the associated punch sensor while all other data locations in that column are passing by the associated punch sensors, a problem can still exist in that even the slightest misorientation or skew between the column being read and the detector array will prevent the sensor signals from occurring simultaneously. That is, assume that a particular data column includes a first data punch in the uppermost data location and a second data punch in the lowermost data location and further that the column passes by the sensor array skewed such that the leading edge of the uppermost data punch reaches the sensor array prior to the arrival of the leading edge of the lowermost data punch. In this situation, the electrical signal produced by the uppermost data punch occurs at a time prior to the time at which the signal is produced by the lowermost data punch. Thus, although the time duration of the two punch-indicating signals can be such that there exists moments in time in which both signals are present, the two signals are not truly simultaneous with one another (i.e., the signals are not in phase with one another).
The failure of the signals to be in phase with one another is often undesirable or completely incompatible with conventional utilization devices which require input information recorded on punched cards. For example, if the output signals of 12 optical sensors are to be utilized as a 12 bit parallel data word and the card is misaligned relative to the sensor array, the signals representing each bit location are not provided in phase with one another, or even provided with a constant phase relationship between the signals. Thus, the loading of the data, for example, into a digital latch circuit or a register of the utilization device becomes extremely difficult or impossible. This difficulty occurs since, in effect, the utilization device has no means of determining at which instant of time a valid signal is present.
Another difficulty with prior art dynamic card readers has been obtaining a suitable output signal that validly represents the characters encoded in the card columns when the card does not move by the sensor array at a uniform rate. In particular when a card passes by a sensor array at a non-uniform rate, the pulse width of the signal supplied by a sensor in response to a punched data location and the time duration between signal pulses supplied in response to two or more card columns having a punch in the same data location varies with changes in the rate at which the card moves. Accordingly, movement of a card through a dynamic card reader at a nonuniform rate effectively causes perturbations in the sensor output signals that hamper validly interrupting the encoded character represented by these signals. It will be recognized that this problem is especially acute in manually operated dynamic card readers wherein an operator pulls or pushes the card past the sensor array, since in many prior art dynamic readers the operator can not only move the card at a non-uniform rate, but may stop and start the card several times before the encoded data columns each pass by the sensor array. Further, it will be recognized that the signal disturbances caused by improper alignment of the card and sensor array, and the signal disturbances caused by movement of the card at a non-uniform rate, are collective in that the effects of both conditions combine to detrimentally effect the signals supplied by the sensor array.
Accordingly, it is an object of this invention to provide an apparatus and method for the dynamic reading of punched cards that is compatible with all conventional apparatus utilizing the information recorded on such cards.
It is another object of this invention to provide an apparatus and method wherein the punched data recorded on a card is read in a synchronous manner to supply a digital signal suitable for use by conventional digital processing equipment.
It is yet another object of this invention to provide a dynamic card reading apparatus and method for synchronously reading data recorded in columnar format on a card that is suitable for use in situations in which the data columns are not necessarily maintained in perfect alignment with an array of punched detecting devices.
It is still another object of this invention to provide a dynamic card reading apparatus and method for synchronously reading punched cards in situations in which the punched cards are not necessarily moved past the punch sensor array with a uniform velocity.